Yes, a lens stopped down to its maximum aperture (f/22 for your lens, f/64, even f/90 for a view camera lens!) begins to get a bit soft because of diffraction. You do get more depth of field, at the cost of reduced sharpness. Photographers always have to do a balancing act to achieve the "ideal" image.

The sideways "8" on the lens barrel is the infinity mark. Also, most lenses stop at infinity when you focus manually, though some telephotos go
slightly
beyond infinity to compensate for expansion or contraction of the lens material in extreme temperature conditions.

Ok, so how does the effect of softness due to diffraction compare to the out of focus due to using a larger aperture? Do you know of anywhere that I can see examples of the two effects to help me make the decision?